1. Field of the Invention
The present invention relates generally to a dust-proof device for a machine tool, and more particularly to a multi-link telescopic cover.
2. Description of the Related Art
FIG. 1 shows a conventional dust-proof cover including shield plates 10, 11, 12 . . . with various sizes, which are fitted in sequence. To extend the dust-proof cover, the first shield plate 10 is drawn to draw the second shield plate 11, and then the second shield plate 11 draws the third shield plate 12 . . . . The shield plates of the conventional dust-proof cover move asynchronously in extension and telescoping that causes the drawbacks hereunder:
1. The shield plates makes loud noise when extending and telescoping. The shield plates impact each other when the large shield plate is moved quickly that causes the shield plates shifting.
2. To avoid the noise, the dust-proof cover is provided with plastic blocks for damping. The blocks are damaged by oil or cutting liquid of the machine tool or by the impact of the shield plates.
3. The impact causes the shield plates to be tilted, so that the dust-proof cover is curved in extension condition. After a time of use, the shield plates may be collapsed.
FIG. 2 shows an improved dust-proof cover, which has shield plates 20, 21, 22 . . . and a set of link assemblies 30, 31 . . . pivoted on the shield plates respectively. In extension of the dust-proof cover, the first shield plate 20 is drawn to move the second shield plate 21 via the first link assembly 30, and then the second shield plate 21 moves the third shield plate 22 via the second link assembly 31 . . . . This dust-proof cover has several drawbacks.
In mechanical principle, the distance of the movement of each shield plate is identical to the angle of swing of the corresponding linkages. In manufacture, there must be tolerances between the linkages and between the linkages and the slide ways, so called liberal allowance to move the shield plates smoothly. As a result, the angle of swing of the linkages on the first shield plate is different from that of on the last shield plate. The difference of the angle of the swing of the linkages is greater when the number of the shield plates is greater. In other words, the shield plates still move asynchronously and still are curved.
The link assemblies also have problem of shifting left or shifting right, so that it still has to be improved.